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A new suspect is being questioned in connection with the bombing of a metro train in St Petersburg which left 14 people dead, a source close to the investigation has said.
The suspect is the ninth person to have been detained on suspicion of having colluded with the bomber, Kyrgyzstan-born Akbarzhon Dzhalilov, since the attack on April 3.
Dzhalilov, 22, was killed in the explosion.
The blast took place between Sennaya Ploshchad and Tekhnologichesky Institut underground stations.
Russia's Anti-Terrorism Committee said they also found and deactivated a bomb - rigged with shrapnel - at another station.
Eight suspects including a woman were arrested on Thursday in connection with the terrorist bombing on St Petersburg's metro, Russian officials have announced.
Earlier in the day police held three suspected accomplices to the attacker, who was named as Kyrgyzstan-born Akbarzhon Dzhalilov, 22. They also deactivated an explosive device in the apartment where they suspects lived.
The latest arrests come after six people were held on suspicion of recruiting the so-called Islamic State and the Al-Nusra Front following Monday's bombing, which killed 14 people.
There has been no claim of responsibility for the attack.
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A St Petersburg underground station closed after a bomb threat on Tuesday has reopened, Russian news agency RIA reported.
Sennaya Ploshchad station was shut earlier after an anonymous call warning of a bomb.
Monday's deadly blast happened on a train as it travelled between Sennaya Ploshchad and Tekhnologichesky Institut underground stations.
One of the underground stations affected by Monday's bombing in St Petersburg has been closed after a bomb threat, Russian emergency officials have said.
The agency said Sennaya Ploshchad station had been shut after an anonymous call warning of a bomb.
The blast on Monday happened on a metro train as it travelled between Sennaya Ploshchad and Tekhnologichesky Institut underground stations, killing 14 people.
The death toll from the St Petersburg metro bombing has risen to 14, Russia's health minister has said.
Veronika Skvortsova said 11 people died at the scene, one died in an ambulance and two in hospital.
She added that 49 people are still in hospital.
Theresa May has condemned the "horrific" bombing in St Petersburg which killed 11 people on Monday.
The prime minister said she had written to Russian President Vladimir Putin to express her condolences for the "absolutely appalling attack".
"Our thoughts must be with the victims and their friends and families," she said.
"This shows the terrible terrorist threat we are all facing.
"I'm very clear, as the people of the UK were after the attack in London, that we will prevail, the terrorists will not win, our values will prevail."
The St Petersburg subway bomber has been identified as a Kyrgyzstan-born Russian citizen, according to Kyrgyz security services.
The Kyrgyz intelligence agency said the suspect was born in Osh, the country's second largest city, in 1995.
Kazakhstan's security services said it was working with Russia to investigate Monday's blast, which killed 11 people.
The St Petersburg metro explosion has been condemned as a "barbaric and cowardly terrorist attack" by the UN Security Council.
Offering condolences to the victims of the blast - which happened between Sennaya Ploshchad and Tekhnologichesky Institut underground stations - council members released a statement saying the "perpetrators, organizers, financiers and sponsors of these reprehensible acts" should be brought to justice.